Typical blue lasers require cascaded nonlinear conversion, which decreases efficiency. They can also employ a single nonlinear mechanism or stage when operating on a short wavelength of Neodymium (Nd) to Ytterbium (Yb). However, suppression of the gain peaks, in the 1-micron spectral region, is difficult and generally requires optical filtering techniques, which limits the overall power and energy which can be achieved. Operating Yb at 975 nm, similar to operating a Nd-doped laser at 911 nm, suffers from parasitic lasing effects and amplified spontaneous emission (ASE) due to the high gain at the 1030 nm and 1064 nm gain peaks, respectively. In order to operate on the shorter wavelength transitions, the losses in the 1-micron region must be suppressed. This can be done with external filtering. However, at high power intensities and inversion levels, the gain in the 1-micron transition can often overcome the losses, thus limiting power scaling on the short wavelength transition.
Silica based Yb-doped fiber lasers have been used to generate efficient 1-micron light. Photonic crystal fibers have enabled energy scaling to >25 mJ level, and have even been used to generate 975 nm light. However, suppression of the 1030 nm peak, in Yb-doped fibers, is challenging. In view of the above drawbacks, there still remains a need for lasers which have increased efficiency.